CN112469892A

CN112469892A - Thermal insulation device for exhaust gases of a heat engine

Info

Publication number: CN112469892A
Application number: CN201980048548.4A
Authority: CN
Inventors: E·杜马斯
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2018-07-23
Filing date: 2019-07-22
Publication date: 2021-03-09
Also published as: FR3084109B1; WO2020020828A1; FR3084109A1; EP3827161A1

Abstract

An arrangement (100) for circulating the exhaust gases of a heat engine of a motor vehicle, comprising an exhaust manifold (14) comprising an outlet duct (26) and attached to a cylinder head (10) of the engine, in which cylinder head an exhaust duct (12) is formed, each of said ducts being connected at one end to a combustion chamber and at the other end opening into an exhaust chamber (40) of the exhaust gases, said chambers being covered by the walls of the manifold, characterized in that the walls of the chamber (40) are thermally insulated.

Description

Thermal insulation device for exhaust gases of a heat engine

Technical Field

The present invention relates to a motor vehicle heat engine or internal combustion engine.

The invention relates more particularly to a heat engine exhaust circuit.

The invention relates more particularly to an optimized exhaust manifold device for a heat engine.

Background

As is known, a motor vehicle propulsion unit may comprise a heat engine, and means for removing pollutants from the exhaust gases generated by the operation of said engine. The pollutant removing means is selected from the list comprising, for example, a catalytic converter, a particulate filter, a nitrogen oxide trap. In particular, the pollutant emissions of motor vehicles equipped with combustion engines are subject to increasingly stringent standards. According to the combustion engine technology in question, the pollutants whose emission thresholds are regulated are carbon monoxide (CO), unburned Hydrocarbons (HC), nitrogen oxides (NOx) and particulates. It is known practice to use a number of pollutant removing devices in the exhaust line of a combustion engine in order to thereby limit the emission of regulated pollutants. For example, oxidation catalytic converters make it possible to treat carbon monoxide, unburned hydrocarbons and, under certain conditions, also nitrogen oxides; particulate filters may be used to treat soot particles. Specific devices for treating nitrogen oxides or NOx are also known, such as NOx traps or catalytic converters known as SCR (selective catalytic reduction). This latter technique consists in reducing NOx by introducing a reducing agent into the exhaust gases. The generated reductant allows the reduction of nitrogen oxides by reaction in an SCR catalytic converter (that is, a substrate bearing a catalytic impregnate capable of promoting the reduction of NOx by the reductant).

A multicylinder internal combustion engine of a motor vehicle therefore has a cylinder head of said engine, in which exhaust conduits are arranged, each of said conduits having a first end connected with a combustion chamber, and a second end opening into a cavity or plenum of an exhaust manifold fixed to the cylinder head, said manifold having an outlet conduit externally connected to means for removing pollutants from the exhaust gases of an exhaust line of the vehicle.

Typically, exhaust devices have exhaust gas conduits formed in the cylinder head of the engine that conform to manifold conduits disposed adjacent the exhaust gas conduits. The manifold has at least one outlet conduit connected to an exhaust line of the motor vehicle.

In order to reduce the content of pollutant products in the combustion gases, it is known practice to install a pollutant removal device, in particular a catalytic converter, in the exhaust line downstream of the exhaust manifold in the direction of circulation of the gases, which makes it possible to convert the pollutant products present in the combustion gases, in particular the unburned hydrocarbons HC and the nitrogen oxides NOx.

However, the effectiveness of the contaminant removal device is highly dependent on the temperature of the gas.

One of the factors that affects the temperature of the gas at the pollutant removing device is the distance between the combustion chamber and the device. In particular, the distance of these pollutant removing means from the combustion chamber of the engine delays the rise of its temperature, especially during the first few minutes of operation of the engine, reducing its effectiveness, even if the amount of pollutants emitted is maximal during these first few minutes of operation of the engine.

This drawback is overcome by realising an exhaust manifold partially or totally integrated in the cylinder head of the engine, so as to substantially reduce the distance between the combustion chamber and the pollutant removing means.

Document FR 2738289 describes in particular an exhaust manifold of this type. The exhaust conduit of the cylinder head leads to a cavity or plenum, half of which is formed in the cylinder head and half in the manifold.

However, the manifold joined to the cylinder head is subject to high temperature stresses and, like the material of the cylinder head, undergoes significant expansion as its temperature increases. As a result, it is practically impossible to couple such a manifold to the rest of the exhaust line unless it is equipped with a cooling cavity of a coolant circulation circuit connected to the cylinder head.

However, cooling of the manifold has a significant negative impact on the efficiency of the engine. Cooling of the manifold reduces the thermal efficiency of the engine. In addition, the cooling also substantially reduces the benefit of the manifold and combustion chamber being closer together. In particular, the cooling of the manifold no longer allows a rapid increase in the gas temperature suitable for increasing the effectiveness of the pollutant removing means.

To remedy this drawback, document FR 2902827-a1 proposes a device having a manifold fixed to the cylinder head of the engine and equipped with means for thermally uncoupling it from said cylinder head. According to this document, the manifold has a portion integrated in the cylinder head, said portion being in contact with the cylinder head at a plurality of different fixing points. Insulation is formed by an air gap. The fixation of the manifold to the cylinder head is formed by a mechanical connection between the manifold and the other parts. These mechanical linkages expand under the heat of the combusted gases, causing thermal cycling and mechanical stresses.

The object of the present invention is to remedy these problems and one of the subjects of the invention is a device for circulating the exhaust gases of a motor vehicle heat engine comprising an exhaust manifold fixed to the cylinder head of the engine, said manifold being partially integrated in the cylinder head, the cavity or plenum to which the exhaust ducts of the cylinder head open being delimited by a recessed wall in the cylinder head and the wall of the manifold. The manifold also has an outlet conduit connected to a contaminant removal device. The walls defining the plenum are thermally insulating walls for maintaining the temperature of the gases as they pass through.

Disclosure of Invention

The invention relates more particularly to a device for circulating the exhaust gases of a motor vehicle heat engine, comprising an exhaust manifold having at least one outlet duct and fixed to the cylinder head of the engine, in which exhaust ducts are hollowed out, each of these ducts being connected at one end to a combustion chamber and at the other end opening into an exhaust gas chamber, said chambers being covered by the walls of the manifold, characterized in that the walls of the chambers are thermally insulated.

Advantageously, the walls of the exhaust gas chamber (which form a plenum to which each exhaust conduit hollowed out in the cylinder head opens) are thermally insulated to avoid any thermal loss of the gases and to make it possible to obtain the highest possible temperature of the exhaust gases, depending on the operating speed of the engine, as they enter the pollutant removing means.

In this way, the contaminant removal device may have optimal effectiveness.

Furthermore, the walls of the manifold are less affected by the temperature of the gas, thus inhibiting the expansion of the manifold.

According to a further feature of the present invention:

the downstream end of each of the exhaust conduits leading towards the exhaust chamber is thermally insulated.

Advantageously, the downstream end of each exhaust conduit of the cylinder head is thermally insulated to avoid any warming of the mouth of each exhaust conduit of the cylinder head, which might lead to warming of the manifold.

-the upstream end of the outlet conduit of the manifold is thermally insulated.

Advantageously, the upstream end of the outlet conduit of the manifold (said end facing the exhaust chamber) is thermally insulated to avoid any warming of the walls of the manifold surrounding the exhaust chamber and to reduce the differential expansion of the manifold with respect to the cylinder head.

The inner wall of the venting chamber is covered with a thermally insulating sheath.

Advantageously, the exhaust chamber or plenum is defined by a thermal insulation jacket covering the entire exhaust chamber. Thus, the heat jacket is contained within a chamber formed by the walls of the cylinder head and the exhaust manifold. The thermal jacket thus insulates the exhaust manifold from the burnt gases and allows to reduce the rise in temperature of said manifold and therefore its expansion.

The insulating jacket comprises an upstream half-shell joined to the wall of the exhaust cavity of the cylinder head, each of the exhaust ducts emerging from the exhaust cavity.

Advantageously, the insulating sheath comprises an upstream half-shell in the direction of flow of the gas, joined to a fixed wall of a cylinder head from which the exhaust conduit emerges. The half-shell has a shape substantially complementary to the shape of the exhaust wall of the cylinder head, obtained for example by a recess from the fixed wall of the cylinder head, so as to form a cavity for increasing the volume of the exhaust chamber, or optimally reducing the body of the exhaust manifold, and enable the pollutant removing means to be brought closer to the combustion chamber of the engine.

The upstream half-shell has, for each exhaust duct, a sleeve, each of the sleeves being pushed into the downstream end of the exhaust duct.

Advantageously, the upstream half-shell has a bushing, at least one bushing per exhaust conduit of the cylinder head, which is pushed into the downstream end of said exhaust conduit, so that said half-shell can be retained by the cylinder head, and also allows optimum insulation of the walls forming the exhaust chamber or plenum, to reduce the temperature of the fixed walls of the cylinder head and of the manifold fixed to the cylinder head by said walls, so as to reduce the difference in expansion of the cylinder head and the manifold.

The jacket has a downstream half-shell joined to the wall of the exhaust manifold.

Advantageously, the thermal insulating sheath has a downstream half-shell joined to the wall of the exhaust manifold, said half-shell being intended to come into contact with the exhaust gases in order to reduce the heating up of the wall of the manifold and also to reduce the drop in temperature of the exhaust gases.

The downstream half-shell has at least one outlet bushing pushed into the outlet duct of the exhaust manifold.

Advantageously, the downstream half-shell has at least one outlet bushing pushed into at least one outlet duct of the manifold leading to pollutant removing means of the engine. The outlet sleeve makes it possible to mechanically retain the half-shell in the exhaust manifold.

The outlet conduit of the manifold has a stop for receiving the free end of the at least one outlet cannula.

Advantageously, at least one outlet duct of the manifold has a stop able to receive the free end of at least one outlet cannula in order to ensure optimal positioning of the half-shell in the wall of the manifold.

-the upstream half-shell and the downstream half-shell are made of the same material and/or form the insulating sheath integrally.

Advantageously, the upstream half-shell and the downstream half-shell are made of the same material and/or are integrally formed with an insulating sheath, so as to make it easier to obtain the half-shells and to fit the insulating sheath between the cylinder head and the exhaust manifold.

-the insulating sheath is firmly fixed to the manifold.

Advantageously, the sheath is firmly fixed to the manifold by means of, for example, a strip which surrounds the upstream half-shell to press it against the downstream half-shell to hold the insulating sheath formed by the two half-shells against the wall of the manifold, with at least one outlet bushing being pushed into at least one outlet duct of the manifold. The insulating sheath is then correctly fixed to the manifold, so as to make it easier to fit the assembly against the fixed wall of the cylinder head.

The insulating sheath comprises a layer of mineral insulating material covered with a thin metal wall.

Advantageously, the insulating sheath comprises a layer of mineral insulating material covered with a thin wall to ensure that the structure of the insulating sheath is maintained. In particular, the thin wall is sufficiently rigid to maintain the shape of the jacket, and the layer of mineral insulating material can then be deformed so as to closely fit the walls of the exhaust chamber (i.e. the walls of the cylinder head and the walls of the manifold).

The thin metal wall is intended to be in contact with the exhaust gases.

Advantageously, the thin metal wall is intended to be in contact with the exhaust gases, making it possible to maintain the shape of the chamber containing the exhaust gases during operation of the engine and to protect the insulating layer from any damage.

The insulating material layer is compressed into contact with the inner wall of the exhaust chamber.

Advantageously, the layer of mineral insulating material is compressed in contact with the walls of the exhaust chamber, in particular against the walls of the exhaust cavity of the cylinder head, the walls of the downstream end of each exhaust conduit of the cylinder head, and the walls of the upstream end of the outlet conduit of the manifold, so as to allow an optimal thermal insulation of the exhaust gas flow flowing through the exhaust manifold with the exhaust gas flow.

Drawings

Further characteristics and advantages of the invention will become apparent from reading the following description of a particular embodiment of the invention, given by way of non-limiting example and illustrated in the accompanying drawings, wherein:

fig. 1 is a schematic view of an exhaust face of a heat engine having a contaminant removal device.

FIG. 2 is a schematic illustration of an exhaust face of a heat engine having an exhaust manifold.

Fig. 3 is a schematic longitudinal sectional view of an apparatus for circulating exhaust gas according to the present invention.

Fig. 4 is a schematic cross-sectional top view of an apparatus for circulating exhaust gas according to the present invention.

Fig. 5 is a schematic view of an insulating sheath of an apparatus for circulating exhaust gas according to the present invention.

Detailed Description

In the following description, like reference numbers indicate identical or functionally similar elements.

The term upstream/downstream refers to the direction of circulation of the exhaust gas.

As is known, according to fig. 1 and 2, a heat engine (not shown) comprises a cylinder head 10 arranged above a crankcase (not shown). In the crankcase, the cylinder is hollowed out along a substantially vertical axis orthogonal to the joint plane 11 of the cylinder head to the crankcase. In the cylinder head 10, an exhaust duct 12 is hollowed out connecting the combustion chambers, each of said chambers being delimited by one of the cylinders, by an engagement plane or by a substantially conical top portion recessed in the cylinder head from the engagement plane and facing the cylinder, and by a piston (not shown) able to slide reciprocally along the axis of said cylinder. Each of the exhaust conduits is able to direct combusted or exhaust gases towards an exhaust manifold 14 which is fixed to the cylinder head against a fixed wall 17 which turns towards a so-called exhaust face 13 of the cylinder head 10. Each of the exhaust conduits leads from the cylinder head through the fixed wall 15 to an exhaust chamber or plenum delimited downstream by the wall of the exhaust manifold 14 in the circulation direction of the exhaust gases.

The combusted gases produced by the combustion in the combustion chamber are thus directed via the exhaust conduit to pass through the exhaust manifold 14 and to the turbine stage 15 and the pollutant removal device 16, as shown in fig. 1, thereby defining a direction of circulation of the exhaust gases. The circulation of the gas is indicated by arrows 34 in fig. 3 and 4.

The present invention relates to an arrangement 100 for recycling exhaust gases from a combustion chamber to a pollutant removing device. The device 100 includes an exhaust conduit 12 hollowed out in the cylinder head, a plenum chamber, and an exhaust manifold 14, with the outlet conduit connected to a contaminant removal device.

In order to reduce the travel distance of the exhaust gases from the combustion chamber to the pollutant removing means 16, in a known manner, the fixed wall 17 is recessed so as to form an exhaust cavity 18 of the cylinder head 10, said cavity 18 being covered by the manifold 14, as shown in fig. 4. The manifold 14 covers the exhaust cavity to form an exhaust chamber 40 for the gases or a plenum chamber for the exhaust gases.

According to fig. 3 and 4, which illustrate a preferred embodiment of the invention, the walls of the exhaust chamber 40 are thermally insulated; in particular, the inner wall 19 of the chamber is covered with a thermal insulating sheath 20. Said walls of the chamber are formed by the walls 33 of the exhaust cavity 18 and the walls 32 of the manifold 14. The insulating sheath 20 is formed by a first upstream half-shell 21, joined to the wall of the exhaust cavity 18 of the cylinder head 10, and by a second downstream half-shell 22, pressed against the wall 32 of the exhaust manifold 14 inside the manifold.

The jacket allows thermal insulation via the interior of the exhaust chamber 40 in order to maintain the temperature of the gas and avoid thermal losses, thereby improving the effectiveness of the downstream pollutant removal means, and protects the walls of the exhaust chamber 40 (in particular the walls 19 of the exhaust cavity 18) and of the manifold 14 from rising to high temperatures that tend to cause differences in expansion and stress in the means of fixing the manifold to the cylinder head.

According to one embodiment, the first half-shell 21 and the second half-shell 22 are formed of the same material, by a layer 23 of mineral insulating material of the mineral fibre MAT (MAT) type, to which a thin metal wall 24 is attached. Said thin metal wall 24 faces the interior of the chamber and is intended to be in contact with the exhaust gases. The metal layer makes it possible to ensure an optimal shape for guiding the exhaust gases towards the outlet duct. The insulating layer can be compressed and the thickness of the thin metal layer has no substantial effect on the total volume of the exhaust chamber, thereby making it possible to house the body of the apparatus 100 for circulating gas. According to a preferred embodiment, the mineral fibers may be based on calcium silicate in order to withstand the temperature levels of the exhaust gases.

The first upstream half-shell 21 has an inlet bushing 25 with dimensions substantially complementary to those of the exhaust duct 12, said inlet bushing 25 being intended to be pushed into said exhaust duct 12. The upstream half-shell 21 has an inlet bushing 25 (as many exhaust conduits 12 as the cylinder head has and more precisely as many mouths 12f of the exhaust conduits 12 in the exhaust cavity 18). In particular, according to fig. 4, each cylinder is connected to the exhaust cavity 18 by a plurality (in this case two

initial ducts

12a, 12b) which are then combined into a single downstream end duct 12c leading to the exhaust cavity 18. For ease of understanding, the remainder of this description refers to a single exhaust conduit 12 per cylinder. According to fig. 3 and 4, the mouth of the exhaust conduit 12 in the wall of the exhaust cavity 18 has a flared mouth 18e for receiving the inlet sleeve 25.

Advantageously, the fitting of the inlet sleeve 25 in the exhaust duct 12 (in particular in the flared mouth 18e of said duct 12) allows the upstream half-shell 21 to be mechanically retained in the exhaust cavity 18 and therefore in the cylinder head 10. Furthermore, this arrangement allows an optimum thermal insulation of the discharge chamber 40 or plenum chamber, in order to avoid, among other things, differences in the expansion of the cylinder head 10 and the manifold 14 on the one hand, and to maintain the temperature of the exhaust gases as they pass through the manifold on the other hand.

The second downstream half-shell 22 has an outlet spigot 27 of a size substantially complementary to the outlet conduit 26 of the manifold 14.

However, the exhaust manifold 14 may have a plurality of outlet conduits 26 and may then have as many outlet sleeves 27 as outlet conduits 26 of the manifold.

The outlet sleeve 27 is intended to be pushed into the outlet conduit 26 of the manifold 14. The fitting of the outlet bushing 27 in the outlet conduit 26 allows an optimal insulation of the wall of the manifold 14 and makes it possible to avoid a significant increase in the temperature of the manifold 14. Similarly, the outlet conduit 26 of the manifold 14 has a flared mouth 28 intended to receive an outlet sleeve 27. Said flared mouth is preferably terminated by a stop 29 for receiving the free end of the outlet sleeve 27 in order to ensure the positioning of the second half-shell 22 in the wall of the manifold 14. The stop 29 may be, for example, a circular shoulder recessed into the wall 32 of the manifold 14. The upstream end 26a of the outlet conduit 26 of the manifold is therefore thermally insulated.

The first upstream half-shell 21 has an external groove 30, which is continued by a groove of the same size in the second downstream half-shell 22, so as to allow the two half-shells to be fixed together, for example by a strip, so as to form a single part.

According to another embodiment, the groove 30 allows the strip to be wound so as to allow the first half-shell 21 to be fixed to the manifold 14.

The assembly of the two half-shells may comprise the following steps:

fitting the second half-shell 22 in contact with the inner wall of the manifold, with the outlet cannula 27 pushed into the outlet conduit 26 of the manifold,

fitting the first upstream half-shell 21 in edge-to-edge contact with the second downstream half-shell 22,

fixing the first half-shell 21 to the manifold by attachment of, for example, a strip housed in the groove 30,

fixing the manifold 14 to the fixed wall of the cylinder head 10, with the inlet bushing 25 pushed into the exhaust conduit 12 of the cylinder head.

The insulating layer 23 of the jacket is pressed against the wall of the exhaust cavity of the cylinder head and against the wall of the manifold by a thin metal wall, which thus delimits the internal volume of the chamber from which the gases are discharged.

The object is achieved as follows:

the circulation device 100 provides thermal insulation of the exhaust chamber to maintain the temperature of the gas as it passes through the manifold and reduces the high temperature of the manifold 14, which may cause differential expansion between the cylinder head 10 and the manifold 14, which may cause stress in the fixture.

It goes without saying that the invention is not limited to the embodiments described above by way of example only, but encompasses all variants thereof.

For example, a varnish layer may be present as a thermal insulating material.

Claims

1. An apparatus (100) for circulating the exhaust gases of a motor vehicle heat engine, comprising an exhaust manifold (14) having an outlet duct (26) and fixed to a cylinder head (10) of the engine, in which exhaust ducts (12) are hollowed out, each of said ducts being connected at one end to a combustion chamber and at the other end opening into an exhaust gas exhaust chamber (40), said chambers being covered by a wall of the manifold,

characterized in that the walls of the chamber (40) are thermally insulated.

2. The device (100) as claimed in claim 1, characterised in that the downstream end (12c) of each of the exhaust ducts (12) directed towards the exhaust chamber is thermally insulated.

3. The device (100) according to claim 1 or 2, wherein the upstream end (26a) of the outlet conduit (26) of the manifold is thermally insulated.

4. The device (100) according to any of the claims 1 to 3, wherein the inner wall of the venting chamber (40) is covered with a thermally insulating jacket (20).

5. The device (100) according to claim 4, characterised in that the insulating sheath (20) comprises an upstream half-shell (21) joined to the wall of the exhaust cavity (18) of the cylinder head from which each of the exhaust ducts (12) emerges.

6. The device (100) according to claim 5, characterized in that the upstream half-shell (21) has, for each exhaust duct (12), an inlet bushing (25), each of the inlet bushings (25) being pushed into the downstream end (12c) of the exhaust duct (12).

7. The device (100) according to any one of claims 4 to 6, characterised in that the thermal insulation sheath (20) has a downstream half-shell (22) joined to the wall (32) of the exhaust manifold (14).

8. The device (100) according to claim 7, characterised in that the downstream half-shell (22) has an outlet sleeve (27) which is pushed into the outlet duct (26) of the exhaust manifold.

9. The device (100) according to claim 8, characterised in that the outlet conduit (26) of the manifold has a stop (29) for receiving the free end of the outlet sleeve (27).

10. The device (100) according to any one of claims 7 to 9, characterised in that the upstream half-shell (21) and the downstream half-shell (22) are made of the same material and form the insulating sheath (20) in one piece.

11. The apparatus (100) of claim 10, wherein the insulating sheath (20) is fixedly secured to the manifold (14).

12. The device (100) according to any one of claims 4 to 11, wherein the insulating sheath (20) comprises a layer (23) of mineral insulating material covered with a thin metal wall (24).

13. The device (100) as claimed in claim 12, characterised in that the thin metal wall (24) is intended to be in contact with the exhaust gases.

14. The apparatus (100) of claim 12, wherein the layer of insulating material (23) is compressed into contact with an inner wall of the vent chamber (40).